1. Field of the Invention
The present invention relates to a cooling fan controller and a liquid crystal projector.
2. Description of the Prior Art
A liquid crystal panel, a light source lamp for backlight arranged on a rear surface of the liquid crystal panel, a signal processing circuit, and a power supply circuit are provided inside a casing of a liquid crystal projector. Further, a cooling fan for cooling the liquid crystal panel, the light source lamp for backlight, and so forth is provided inside the casing of the liquid crystal projector. Conventionally, the higher the rotational speed of the cooling fan is, the more the cooling efficiency increases, but the more noise increases.
Therefore, a technique for detecting a temperature in the liquid crystal projector by a temperature sensor arranged in the casing and controlling the rotational speed of the cooling fan on the basis of the detected temperature has been developed. That is, the cooling fan is controlled such that the rotational speed of the cooling fan is reduced when the temperature in the liquid crystal projector (hereinafter referred to as interior temperature) is low, while being increased as the interior temperature increases.
FIG. 5 illustrates the relationship between a voltage for driving a motor for driving the cooling fan (hereinafter referred to as a fan motor) and the number of revolutions (the rotational speed).
In FIG. 5, V1 represents a minimum voltage required to rotate the fan motor from a stopped state (hereinafter referred to as a minimum voltage for fan starting). After the fan motor is rotated once, it can be rotated even if the driving voltage is dropped in a range from a predetermined voltage V0 lower than the minimum voltage for fan starting V1 to the voltage V1. V0 represents a minimum voltage for fan control, and V2 represents a maximum voltage for fan control.
Conventionally, a fan motor control voltage (a voltage for driving a cooling fan) V is controlled such that a relationship as shown in FIG. 6 exists between the interior temperature T and the fan motor control voltage V.
The relationship between the interior temperature T and the fan motor control voltage V is as follows:
(1) When the interior temperature T is not more than a set minimum temperature for fan control Ta, the fan motor control voltage V is the minimum voltage for fan starting V1.
(2) When the interior temperature T is more than the set minimum temperature for fan control Ta and is a set maximum temperature for fan control Tb (Tb greater than Ta), the higher the interior temperature T is, the higher the fan motor control voltage V becomes within a range from V1 to V2.
(3) When the interior temperature T is more than the set maximum temperature for fan control Tb, the fan motor control voltage V is V2.
In a case where a power supply to the liquid crystal projector is turned on and in a time period elapsed since the power supply was turned on, the interior temperature is lower than the set minimum temperature for fan control Ta. In the conventional example, however, the fan motor control voltage V cannot be conventionally made lower than the minimum voltage for fan starting V1 irrespective of the fact that the interior temperature T is lower than the set minimum temperature for fan control Ta in the case where the power supply is turned on and in the predetermined time period elapsed since the power supply was turned on. Therefore, noise cannot be further reduced.
An object of the present invention is to provide a cooling fan controller and a liquid crystal projector, in which noise can be reduced.
In a cooling fan controller that controls a voltage for driving a cooling fan on the basis of a temperature detected by a temperature sensor, a first cooling fan controller according to the present invention is characterized by comprising means for controlling the voltage for driving the cooling fan to a minimum voltage for cooling fan starting which is required to start the cooling fan when the cooling fan is started; and means for controlling, on the basis of a predetermined relationship between the detected temperature and the voltage for driving the cooling fan, the voltage for driving the cooling fan to a driving voltage value corresponding to the detected temperature after the cooling fan is started, the relationship between the detected temperature and the voltage for driving the cooling fan being determined such that the higher the detected temperature becomes, the larger the voltage for driving the cooling fan becomes in a range from a predetermined minimum voltage for cooling fan control which is lower than the minimum voltage for cooling fan starting to a predetermined maximum voltage for cooling fan control which is higher than the minimum voltage for cooling fan starting.
In a cooling fan controller that controls a voltage for driving a cooling fan on the basis of a temperature detected by a temperature sensor, a second cooling fan controller according to the present invention is characterized by comprising a circuit for controlling the voltage for driving the cooling fan to a minimum voltage for cooling fan starting which is required to start the cooling fan when the cooling fan is started; and a circuit for controlling, on the basis of a predetermined relationship between the detected temperature and the voltage for driving the cooling fan, the voltage for driving the cooling fan to a driving voltage value corresponding to the detected temperature after the cooling fan is started, the relationship between the detected temperature and the voltage for driving the cooling fan being determined such that the higher the detected temperature becomes, the larger the voltage for driving the cooling fan becomes in a range from a predetermined minimum voltage for cooling fan control which is lower than the minimum voltage for cooling fan starting to a predetermined maximum voltage for cooling fan control which is higher than the minimum voltage for cooling fan starting.
In a liquid crystal projector comprising a temperature sensor that detects the interior temperature of the liquid crystal projector and a cooling fan controller that controls a voltage for driving a cooling fan on the basis of a temperature detected by the temperature sensor, a first liquid crystal projector according to the present invention is characterized in that the cooling fan controller comprises means for controlling the voltage for driving the cooling fan to a minimum voltage for cooling fan starting which is required to start the cooling fan when the cooling fan is started, and means for controlling, on the basis of a predetermined relationship between the detected temperature and the voltage for driving the cooling fan, the voltage for driving the cooling fan to a driving voltage value corresponding to the detected temperature after the cooling fan is started, the relationship between the detected temperature and the voltage for driving the cooling fan being determined such that the higher the detected temperature becomes, the larger the voltage for driving the cooling fan becomes in a range from a predetermined minimum voltage for fan control which is lower than the minimum voltage for cooling fan starting to a predetermined maximum voltage for cooling fan control which is higher than the minimum voltage for cooling fan starting.
In a liquid crystal projector comprising a temperature sensor that detects the interior temperature of the liquid crystal projector and a cooling fan controller that controls a voltage for driving a cooling fan on the basis of a temperature detected by the temperature sensor, a second liquid crystal projector according to the present invention is characterized in that the cooling fan controller comprises a circuit for controlling the voltage for driving the cooling fan to a minimum voltage for cooling fan starting which is required to start the cooling fan when the cooling fan is started, and a circuit for controlling, on the basis of a predetermined relationship between the detected temperature and the voltage for driving the cooling fan, the voltage for driving the cooling fan to a driving voltage value corresponding to the detected temperature after the cooling fan is started, the relationship between the detected temperature and the voltage for driving the cooling fan being determined such that the higher the detected temperature becomes, the larger the voltage for driving the cooling fan becomes in a range from a predetermined minimum voltage for cooling fan control which is lower than the minimum voltage for cooling fan starting to a predetermined maximum voltage for cooling fan control which is higher than the minimum voltage for cooling fan starting.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.